Full text of "USPTO Patents Application 10687850"

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IDIlIIllllllOlllll

(H) EP 1 275 732 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) , nt C |/ : C12Q 1/00, G01N 33/487

15.01.2003 Bulletin 2003/03

(21 ) Application number. 02012365.9

(22) Date of filing: 06.06.2002

(84) Designated Contracting States:

(72) Inventor: Charlton, Steven C.

AT BE CH CY DE DK ES R FR GB GR IE IT LI LU

Oseceola, IN 46561 (US)

MCNLPTSETR

Designated Extension States:

(74) Representative: Burkert, Frank et al

AL LTLVMK RO SI

Bayer AG,

Konzernbereich RP

(30) Priority: 11.06.2001 US 296910 P

Patente und Lizenzen

51368 Leverkusen (DE)

(71) Applicant: Bayer Corporation

Pittsburgh, PA 15205 (US)

(54) Electrochemical test sensor with an underfill detection system

(57) A test sensor having a pair of electrodes and a the capillary channel. The liquid test sample is collected

reagent for eiectrochemically measuring the concentra- and moved through the capillary channel. The liquid test

tion of the analyte in a liquid sample. The test sensor sample contacts the conductor when the capillary chan-

comprises a capillary channel for collecting the liquid nel is substantially full to signal a full condition,
sample and a conductor disposed outside the capillary
channel. The conductor is in fluid communication with

Europaisches Patentamt
European Patent Office
Office europeen des brevets

CM
CO

Q.
LU

Printed by Jouve. 75001 PARIS (FR)

EP 1 275 732 A1

Description

FIELD OF THE INVENTION

(0001 ] The present invention relates generally to elec-
trochemical biosensing lor quantifying a specific com-
ponent (analyte) in a liquid sample, and more particu-
larly, to an underfill detection system for use with an
electrochemical biosensor.

BACKGROUND OF THE INVENTION

[0002] It Is often necessary to quickly obtain a sample
of blood and perform an analysis of the blood sample.
One example of a need for obtaining a sample of blood
is In connectionwith ablood glucose monitoring system,
which a user must frequently use to monitor the user's
blood glucose level.

r0003] Those who have irregular blood glucose con-
centration levels are medically required to regularly self-
monitor their blood glucose concentration level. An ir-
regular blood glucose level can be brought on by a va-
riety of reasons including illness such as diabetes. The
purpose of monitoring the blood glucose concentration
level is to determine the blood glucose concentration
level and then to take corrective action, based upon
whether the level is too high or too low, to bring the level
back within a normal range. The failure to take corrective
action can have serious implications. When blood glu-
cose levels drop too low - a condition known as hypogly-
cemia - a person can become nervous, shaky, and con-
fused. That person's judgment may become impaired
and that person may eventually pass out A person can
also become very ill if their blood glucose level becomes
too high - a condition known as hyperglycemia. Both
conditions, hypoglycemia and hyperglycemia, are po-
tentially life-threatening emergencies.
roo04] One method of monitoring a persons blood
glucose leveliswithaportable.hand-heldbloodglucose

testing device. The portable nature of these devices en-
ables the users to conveniently test their blood glucose
levels at anytime or in any place the user may be. The
glucose testing device includes a test sensor to harvest
the blood for analysis. Such a test sensor is described
in U S Patent No. 5.759,364. which is entitled "Electro-
chemical Biosensor." In order to check the blood glu-
cose level, a drop of blood is obtained from the fingertip
using a lancing device. The blood drop is produced on
the fingertip and the blood is harvested using the test
sensor. The test sensor, which is inserted into a testing
unit is brought into contact with the blood drop.Thetest
sensor draws the blood to the inside of the test unit
which then determines the concentration of glucose In
the blood. Once the results of the test are displayed on

a display of the test unit, the test sensor is discarded.

Each new test requires a new test sensor.

[0005] One problem associated with some lancing

and/or testing devices is that the requisite amount ot

blood for accurate test results is not always obtained
Roughly thirty percent of lances do not produce enough
blood for analysis. The amount of blood obtained from
each lance varies between zero and ten microliters. For
s an accurate result, at least two microliters of blood must
be obtained. If less than this amount is obtained, the test
results may be erroneous and a test sensor is wasted.
More serious an issue, however, Is that the user may be
relying on inaccurate results when an insufficient sam-
w pie volume is harvested. Obviously, because of the se-
rious nature of the medical issues involved, erroneous
results are to be avoided.

[0006] Anotherproblem associated with conventional
lancing devices is that there is no mechanism to let the
15 user know whether the correct amount of blood has
been obtained for accurate analysis. Typically, the test
units come with instructions graphically illustrating the
size of the blood drop required for accurate testing.
However, this visual comparison is subjective and often
20 produces inconsistent results. To insure the requisite
amount of blood is produced, users often overcompen-
sate by squeezing or otherwise manipulating theirhnger
to produce a larger than necessary drop of blood. How-
ever, this adds time to the overall testing process and
25 also results in an increased amount of wasted blood. It
is preferable to require/obtain as little of the user's blood
as possible for accurate results. Put another way, it is
desirable to only obtain the required amount of blood.
Often, requiring an increased amount of blood trans-
30 lates into a more "invasive" procedure meamng that the
obtaining of the same can take more time and be more
painful. Accordingly, their exists a need for a blood glu-
cose testing device having an underfill detection system
that can determine whether a correct blood sample vol-
35 ume has been obtained.

SUMMARY OF TH E INVENTION

[0007] A test sensor having a pair of electrodes and
40 a reagent for electrochemically measuring the concen-
tration of the analyte in a liquid sample The test sensor
comprises a capillary channel for collecting the l.qu.d
sample and a conductor disposed outside the capillary
channel. The conductor is in fluid communication with
45 the capillary channel. The liquid test sample is collected
andmoved through the capillary channel. The liquid test
sample contacts the conductor when the capillary chan-
nel is substantially full to signal a full condition.
[0008] The above summary of the present invention
so is not intended to represent each embodiment or every
aspect, of thepresentinvention.Additionalfeaturesand

benefits of the present invention will become apparent
from the detailed description, figures, and claims set
forth below.

RRIEF DESCRIPT ION OF THE FIGURES
[0009] Other objects and advantages of the invention

EP 1 275 732 A1

will become apparent upon reading the following de-
tailed description in conjunction with the drawings in
which:

FIG. 1 is an exploded view of a lid and a base plate
of a test sensor according to one embodiment of the
present invention;

FIG. 2 is a perspective view of a sample collection
end of the base plate illustrated in FIG. 1;
FIG. 3 is an exploded view of a lid, a spacer, and a
base plate of a test sensor according to an alterna-
tive embodiment of the present invention; and
FIG. 4 is an exploded view of a lid, a spacer, and a
base plate of a test sensor according to another al-
ternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED
EMBODIMENTS

[0010] As discussed in the background section, test
sensors are commonly used to measure the amount of
glucose in a person's blood. One type of sensor for use
in the determination of a person's blood glucose level is
an electrochemical sensor. Such a sensor is described
in commonly owned U.S. Patent No. 5,759,364, which
is incorporated herein by reference in its entirety. Other
types of sensing include colorimetric sensing, which is
described in commonly owned U.S. Patent No.
5,723,284, which is incorporated herein by reference in
its entirety.

[001 1 J Referring now to FIG. 1 , there is shown a test
sensor 10 according to one embodiment of the present
invention. The test sensor 10 includes a base plate 12
and a lid 14. The base plate 12 includes a working elec-
trode 16 and a counter-reference electrode 18 printed
on the surface of the base plate 12. The lid 14 includes
a raised portion 20, the underside of which forms three
side of a capillary channel 22. The base plate 12 forms
the fourth side of the capillary channel 22 when the lid
14 is mated to the base plate 1 2. The base plate 1 2 also
includes a reaction area or test area 24 that is generally
illustrated with a dashed line. The circular area indicated
by the dotted line is shown greater detail in FIG. 2.
[0012] Referring also to FIG. 2, a sample collection
end 25 of the base plate 12 is shown. The base plate
1 2 includes a reagent 26 incorporated into the test area
24. The reagent 26 is designed to react with the glucose
in blood 28 that has moved though the capillary channel
22 to the test area 24. This reaction produces a change
in current across the electrodes 16,18 that is indicative
of the concentration of glucose in the sample of blood.
Put another way, the reaction of glucose and the reagent
creates an oxidation current at the electrodes 16,18
which is directly proportional to the user's blood glucose
concentration. This current can be measured by an ap-
propriate meter (not shown) electrically coupled to a pair
of terminals 30,32 corresponding to the electrodes
16,18.

[0013] In operation, the user lances the user's finger-
tip to produce a sample of blood. The test sensor 10 is
typically inserted into a testing device, with the sample
collection end 25 exposed. The sample collection end

5 25 is brought into contact with the blood sample. Blood
moves, via capillary action, from the collection end 25
of the sensor 10 into the test area 24 wherein the blood
mixes and reacts with the reagent. As the blood moves
up the capillary channel 22, displaced air vents from the

io capillary channel 22 via a vent hole 34. The ensuing re-
action produces a change in current that is measurable
across the electrodes 16,18. The change in current is
measured by a meter that is coupled to the terminals
30,32.

is [0014] As discussed in the background section, there
exists a need for a test sensor that signals whether a
sufficient sample volume has been collected by the sen-
sor. To detect when a sufficient sample volume is col-
lected, the test sensor is equipped with a third electrode

20 - a signal electrode. For reasons detailed below, the sig-
nal electrode Is not printed on the base plate 12 nor
placed on the under surface of the lid 1 4 so that the sig-
nal electrode faces the capillary channel 22. Rather, a
conductor 36 is formed on the outer surface of the lid 14

25 by coating the outer surface with a conductive material .
The conductor 36 forms the terminal for the signal elec-
trode and the working electrode 1 6 serves as the second
electrode for the signal electrode circuit.
[0015] To form the signal electrode, the vent hole is

30 placed at a distance so that the capillary channel 22,
when filled, provides the necessary volume for a suffi-
cient blood sample to be harvested. The sample has to
make contact with the conductor 36 to signal a full con-
dition. When a sufficient volume of blood moves though

35 the capillary channel 22 into the vent hole 34, the blood
contacts the conductor 36 to form a conductive path be-
tween the conductor 36 and the working electrode 16.
The formation of the conductive path indicates that a
sufficient sample volume is present for accurate testing.

40 According to one embodiment, this path can be part of
a circuit coupled to an LED which is illuminated when
the conductive path is formed. Thus, the user is in-
formed that the requisite volume of blood has been col-
lected.

45 [0016] In order to ease the manufacturing of the test
sensor 10, and more specifically the lid 14 having the
conductor 36, the entire lid 14 is coated with the con-
ductive coating. A line 38 is scribed in the conductive
coating to electrically isolate the conductor 36 from a

so sample collection end 25 of the lid 1 4. When harvesting
a sample of blood, the lid sample collection end 25 (as
well as the base plate collection end 25) contact the
blood sample. If the lid sample collection end 25 was
not isolated from the conductor 36, a conductive path

55 would be formed from one of the conductors 16,18
though the capillary channel 22 to the lid sample collec-
tion end 25 which has been coated with a conductive
coating. Such a conductive path would incorrectly signal

EP 1 275 732 A1

that a sufficient sample has been collected.
[0017] According to one embodiment of the present
invention the conductor 36 is formed by coating the lid

14withafilmofDuPont7102Tcarbontoadry thickness
of 7 urn. The vent hole 34 has a diameter of approxi- 5
mately 0.050 inch (about 0.127 mm). According to an-
other embodiment, the conductor is formed by coating
the ltd 14 with an aluminum film. Methods of covering
the lid 14 with the conductive material include coating
sputter coating, vacuum deposition, and plating. An al- w
ternative to coating the entire lid 14 with a conductive
layer followed by scoring a line 38 to electrically isolate
the conductor 36 from the sample collection end 25 is
to place the conductive material in only the desired area
using techniques such as zone coating, zone sputtering is
and printing. y *
[001 8] As briefly mentioned above, it is undesirable to
print a signal electrode on the base plate 12 because
doing so would effectively increase the volume of the
caprllary channel 22. The capillary channel 22 is de- 20
signed so that only the requisite amount of blood for ac-
curate testing is collected by the test sensor 1 0. Ideally
the signal electrode would be placed at the exact level
of the working electrode 16. However, this is not desir-
able because this arrangement would short out the 25
working electrode 16. Therefore, the signal electrode
must be spaced from the working electrode 16 The in-
ventor has found that, due In part to printing tolerances
spacing the signal electrode away from the working
electrode would require the capillary channel 22 to be so
approximately 0,025 inch (about 0.064 mm) longer. This
in turn increases the capillary area, which translates into
an increased blood sample volume. This is counterpro-
ductive because, as described in the background sec-
tion, it is desirable to minimize the amount of blood re- 35
quired for an accurate analysis.
[001 9] Also mentioned above, is that it is undesirable
to print a signal electrode on the underside of the raised
portion 20 of the lid 14. Due to the relatively confined
capillary channel 22, the surface tension of the blood 40
sample can retard the movement of blood from the col-
lection end 25 of the test sensor 1 0 though the capillary
channel 22 to the test area 24. Therefore, according to
one embodiment, the underside of the raised portion 20
of the lid 14 carries a bifunctional coating that facilitates 45
the movement of the blood though the capillary channel
22. Placing the signal electrode on the underside of the
raised portion 20 of the lid 14 would impede the move-
ment of blood to the test area and increase the overall
time to conduct the test. 50
[0020] Referring now to FIG. 3, an alternative embod-
iment of a test sensor 50 is shown. Whereas the sensor
10 shown in FIG 1 has a "two-piece construction" tie
the base plate 12 and the lid 14), the sensor 50 illustrat-
ed in FIG. 3 has a "three-piece construction" - a base 55
plate 12, a spacer 54, and a lid 56. A "three-piece con-
struction" sensor is described in U.S. Patent No.
5,1 20,420, which is hereby incorporated by reference in

its entirety. The base plate 12 is similar to the base plate
12 illustrated in FIG. 1 in that it includes electrodes 1 6 18
electrically coupled to terminals 30,32, respectively.
Further, a reagent is incorporated into the base plate 12
to react with a blood sample at the test area 24 indicated
generally by dashed lines. The lid 56 includes a vent
hole 52 that allows air to escape from the test sensor 50
when collecting blood.

[0021] The test sensor 50 (FIG. 3) differs from the test
sensor 10 (FIG. 1) in that the lid 56 for the test sensor
50 is not deformed so as to form a capillary channel
Rather, the spacer 54 for the test sensor 50 includes a
cutout which forms a capillary channel 58. The upper
surface of the spacer 54 is coated with a conductive ma-
terial to form a conductor 60. According to one embod-
iment of the present invention, the spacer is formed by
first coating the spacer 54 with the conductive coating
and then cutting the capillary channel 58 in the spacer
54 and conductor 60. The edges of the conductive coat-
ing are exposed to the sample in the capillary channel
58. A line 62 is scribed through the conductor 60 to elec-
trically isolate a sample collection end 64 of the spacer
54 from the conductor 60. Once the sample fills the cap-
illary channel 58 past the line 62, the blood sample con-
tacts the exposed portion (/.a, the sides) of the conduc-
tor 60 to signal a full condition.
[0022] Referring now to FIG. 4, according to an alter-
native embodiment of the test sensor 50 illustrated in
FIG. 3, the lid 56 has a conductor 70 disposed thereon
rather than the spacer 54. The vent hole 52 is positioned
such that when blood fills the capillary channel and
moves though the vent hole 52 to contact the conductor
70 conductive coating on the lid 56 a full condition is
signaled. The conductor 70 is electrically Isolated from
the collection end 64 by a line 72 scribed through the
conductive coating. This embodiment is similar to that
shown in described in connection with FIGS. 1 and 2.
[0023] While the invention is susceptible to various
modifications and alternative forms, specific embodi-
ments thereof have been shown by way of example in
the drawings and herein described in detail. It should be
understood, however, that it is not intended to limit the
invention to the particular forms disclosed, but on the
contrary, the intention is to cover all modifications
equivalents, and alternatives falling within the spirit and
scope of the invention as defined by the appended
claims.

Claims

1 . A test sensor for measuring the concentration of an
analyte in a liquid sample, the test sensor compris-
ing:

a base plate having a pair of electrodes and a
reagent for eiectrochemically measuring the
concentration of the analyte in the liquid sam-

EP 1 275 732 A1

pie; and

a lid having an upper surface, a lower surface,
and a conductor disposed on the upper surface,
the lower surface being mated to the base plate
and forming at least one wall of a capillary chan- s
nel for collecting the sample, the lid having an
aperture for permitting the sample to contact
the conductor to signal a full condition.

2. The test sensor of claim 1 wherein the conductor is to
electrically isolated from a collection end of the test
sample.

3. The test sensor of claim 1 wherein the conductor
comprises a coating of a carbon alloy. is

4. The test sensor of claim 1 wherein the conductor
comprises a coating of an aluminum alloy.

5. The test sensor of claim 1 wherein the base plate 20
includes a terminal coupled to at least one of the
pair of electrodes.

6. The test sensor of claim 1 in combination with a me-
ter adapted to measure a change in current be- 25
tween the pair of electrodes.

7. The test sensor of claim 1 wherein the conductor
comprises a conductive coating disposed on the up-
per surface of the lid, and wherein a line is scribed 30
though the conductive coating to electrically isolat-
ed a first portion of the conductive coating from a
second portion of the conductive coating adjacent

to the sample collection end, the line being dis-
posed between the aperture and the collection end. 35

8. The test sensor of claim 1 in combination with a me-
ter adapted to detect the presence of a conductive
path between one of the pair of electrodes and the
conductor. 40

9. A test sensor for measuring the concentration of an
analyte in a liquid sample, the test sensor compris-
ing:

a base plate having a pair of electrodes and a
reagent for electrochemically measuring the
concentration of the analyte in the liquid sam-
ple;

a spacer having a cutout forming side-walls of so
a capillary channel for collecting the sample;
a lid for forming another wall of the capillary
channel; and

a conductor disposed outside of the capillary
channel for contacting the sample when the 55
capillary channel is substantially full for signal-
ing a full condition.

1 0. A method of determining the concentration of an an-
alyte in a liquid sample with a test sensor, the test
sensor having a pair of electrodes and a reagent for
electrochemically measuring the concentration of
the analyte in the liquid sample, the sensor includ-
ing a capillary channel for collecting the liquid sam-
ple and a conductor disposed outside the capillary
channel, the conductor being in fluid communica-
tion with the capillary channel, the method compris-
ing:

collecting the liquid test sample;
moving the liquid test sample though the capil-
lary channel;

contacting the liquid test sample with the con-
ductor when the capillary channel is substan-
tially full; and

signaling a full condition when the liquid test
sample has contacted the conductor.

EP 1 275 732 A1

European Patent
Office

EUROPEAN SEARCH REPORT

Application Number

EP 02 Gl 2365

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Full text of "USPTO Patents Application 10687850"

See other formats